To realize a memory with a larger capacity, a memory of a spin shift register type that uses domain walls has been suggested. In conventional semiconductor memories, “a storage element, a select element, and an information extracting line” are normally formed in each memory cell. However, this memory of the spin shift register type is based on a concept that only storage elements are arranged at a high density by transferring stored information to the locations of a sensor and a wiring formed in predetermined positions, and such a memory has a possibility of a dramatic increase in memory capacity.
However, a stable shifting operation requires a current with a high current density for the domain walls to transit from a resting state to a moving state. The necessity of a high current and a large amount of power in a shifting operation to be performed frequently is an undesirable aspect in achieving high memory reliability and a smaller power consumption, and the critical current required in a domain-wall shifting operation needs to be lowered.
In a shift register for memories, it is not preferable to provide a control electrode for each bit (or each digit), and a shifting operation needs to be performed on a desired number of digits by applying some effect to the entire bit string. In each shift register that has been suggested for memories, one could manage to shift information in several digits accurately and collectively, but it is not at all easy to shift information in all the digits of information in a magnetic thin wire to realize a large-capacity memory accurately and collectively, which is at least several hundred bits and sometimes can be more than several kilobits to achieve a larger capacity, using the current pulse flowing through the shift register. In a large-capacity memory having a large number of bits in one thin wire, the physical length of the shift register becomes greater, and the possibility of false operations due to rounding of the current pulse waveform caused by the capacity or inductance components might become higher.